After Google's share of the U.S. search market slipped in December, the Mountain View, Calif. company has been trying to entice Firefox users back to the fold.

Firefox users who steer to google.com are being asked if they want to reset their home page to the site or if they would like to change their default search engine to Google.

Computerworld has confirmed the first pitch but not the second; SearchEngineLand first reported on the change-default-search message today.

The move was an obvious response to Mozilla's November deal that made Yahoo the default search engine for most U.S. users of Firefox. Previously, Google was the browser's default, but after the latest contract expired, Mozilla went with Yahoo instead.

That resulted in an almost immediate decline in Google's share of the U.S. search market and a corresponding increase in Yahoo's.

Earlier this month, Irish analytics company StatCounter said that Firefox 34, the version launched Dec. 1 and the first to use Yahoo as its default, was generating four times the search referrals from that search engine than had its predecessor, Firefox 33.

comScore, which publishes monthly stats on search share, echoed StatCounter with its latest data, which was posted Tuesday. According to comScore, Google lost 1.6 percentage points in December, slipping from 67% to 65.4%. Meanwhile, Yahoo gained the same 1.6 points, climbing from 10.2% in November to 11.8% in December.

Google also took a more active approach yesterday, using its official Twitter account to broadcast a "come back" message. That tweet linked to a new page on Google's site that illustrated the steps Firefox users needed to take to switch from Yahoo to Google.

It's unclear how successful the pleas may be, as most research has shown that the vast majority of personal computer users never change default settings of the operating system or applications.

Of course, Google has internal metrics that would show whether Firefox users had deserted in large numbers. Outsiders, however, have no direct insight.

But there's one hint of Google's motivation in StatCounter's latest numbers. For the month of January thus far -- through the 21st -- StatCounter pegged Google's usage share in the U.S. at 74.8%, down slightly from December's 75.3%. Yahoo's usage share had climbed from 10.4% in December to 10.9% so far this month.

Long term it's unlikely that Firefox's Yahoo play will dramatically impact Google, if only because of Firefox's small usage share of the U.S. browser market. For January so far, Firefox accounted for 16.5% of all browser usage, up from 13.6% in December, but far behind Google's own Chrome at 39.7% and Microsoft's Internet Explorer at 33.2%.

Mozilla signed a five-year contract with Yahoo and others with different providers after it dropped Google as its global partner. Financial terms of the deal were not disclosed.

Google is trying to convince Firefox users to switch back from Yahoo with messages like this one, which popped up after browsing to google.com.